use strict;
use warnings;

my @to_merge = 1..$ARGV[0];

my $count = 0;
while (@to_merge > 1) {
   my $qfn_in1 = shift(@to_merge);
   my $qfn_in2 = shift(@to_merge);
   push @to_merge, my $qfn_out = '...';

   $count++;  # open(my $fh_in1, '<', $qfn_in1)
   $count++;  # open(my $fh_in2, '<', $qfn_in2)
   $count++;  # open(my $fh_out, '>', $qfn_out)
}

print("$count\n");